I _think_ the Idiot is referring to line 44x.
"one who will attend to his work and drive a straight furrow and is past the age for gaping after his fellows,  but will keep his mind on his work."
Yes, it's Hesiod, and feel free to pick a different translation (this one has the merit of free access online), but that would seem to be pretty clear: you're looking for a 40 year old so he can pay attention to what he is doing, and plowing straight rather than meandering _because he's paying attention to the other guys out there plowing too_ would appear to be the message. Is Hesiod suggesting that if you hire some young guy you're going to find him out there humperating with the other field hands? Is Hesiod just pointing out that the young'uns are irresponsible twits? Who knows. But suggesting that this is straight-line-vs-terraced is asinine.
Is there some _other_ Hesiod reference to plowing a straight line that I missed? Interpret liberally -- it might amuse me, and I could sure use some amusement at the moment.